In the prior art, an automobile start circuit is such designed that the coil of a start relay is directly connected to automobile batteries, thus, the automobile starts when an ignition switch is turned to the ignition gear. However, the coil of the start relay is still connected to the automobile batteries at that time; in this case, if the main control chip goes wrong and gives a restart signal, the start relay will be closed again to cause the start motor to restart. As a result, the start motor may be easily damaged.